Suggestion of nearby city to go nearby shenzhen or guangzhou

I am travelling from Malaysia to Hong Kong end of Mac 2015 for 2 nites, then proceed to Shenzhen early April 2015 for 2 nites. I intend to stay in GZ for 4 nites at the end of my 11 nites trip. in between Shenzhen and GZ I have extra 3 nites. Can you give me a city or two to visit nearby GZ? What is the best way to travel for sightseeing in these area?